The present invention concerns a hydraulic percussion machine comprising a body containing hydraulic passages and valves and said percussion machine having a gas-filled hydraulic pressure accumulator for storing the energy which accelerates the piston to strike against the tool.
In prior art, several percussion machines are known in which the piston hitting the tool is hydraulically reciprocatingly moved and the impact energy is stored in a high pressure accumulator. In the percussion machine of U.S. Pat. No. 3,965,799, the high pressure accumulator communicates directly with the high pressure conduit and is thus connected in parallel with the high pressure volume, the pressure prevailing there lifting the piston upward. The piston is encircled by a distributor means moving in the same direction as the piston and connecting the space above the piston in alternation to the high pressure passage and the return flow passage. Furthermore, there is a relief in the upper part of the piston, serving as control valve and intended to prevent that the striking movement begins before the piston has reached its top position. When the piston has in its top position stopped against the end position damper, with the pressure control valve continuously closed, the pressure begins to rise in the high pressure accumulator until the pressure opens the pressure control valve. The oil is then admitted to flow through the relief in the piston to the distributor means and lifts it into striking position so that from the pressure line and from the high pressure accumulator high pressure oil can flow to the space over the piston, as a consequence whereof the piston commences its stroke.
The detriment with this apparatus is that one has been compelled to provide the passage from the pressure control valve to the distributor means exactly through the relief in the valve. The relief, and the grooves associated therewith in the body itself merely complicate the design. There is furthermore the risk that the pressure control valve will in fact open before the piston has gone into its top position to open for the pressurized oil the path to the distributor means. When such happens, extra energy will be charged into the high pressure accumulator and, after the piston has gone up, this results in an excessively powerful stroke and in overload on the machine. This leads to damage of the machine's structures. If, again, in the design in question the pressure control valve were totally omitted, the range of operation of the machine would be narrowed, which quite obviously is a major detriment. One more drawback of the percussion machine under consideration is that the energy bouncing back from the tool cannot be recovered in any way: it is converted into both heat and mechanical stresses which act on the structures of the machine. Furthermore, as a result of the design, the return line is subjected to high pressure peaks.
In the percussion machine disclosed U.S. Pat. No. 4,034,817, a purely pneumatic pressure accumulator is used for obtaining the stroke energy. The drawback is then the extra pressure tank, which has been disposed separate from the percussion machine itself. Furthermore, in order to connect the tank with the percussion machine one has been compelled to use an extra pneumatic pressure tube. One further detriment which is difficult to eliminate is the sealing problem between the pressure accumulator and the hydraulic volumes. All these drawbacks detract from the reliability in service; they imply more maintenance work, and they increase the complexity of the machine.